Drug resistance gene transduction of hematopoietic stem cells remains a promising new therapeutic approach in the treatment of the cancer patient. In the proposed clinical trial, hematopoietic progenitor cells from patients with cancer will be isolated on the basis of CD34 immunoselection and transduced with a drug resistance gene a mutant form of MGMT, G156AMGMT. This gene encodes a protein, 06-alkylguaninine-DNA alkyltransferase [AGT], that is resistant to a potent AGT inhibitor, 06-benzylguanine [BG]. BG potentiates the anti-tumor effect of nitrosoureas such as BCNU. It has recently been shown that BG depletes tumor AGT in patients and, when combined with BCNU, myelosuppression is dose limiting. Mouse studies have shown the ability of G156AMGMT transduced marrow cells to protect mice from myelosuppression following BG and BCNU and that up to 1000 fold selection in favor of transduced cells can be achieved following infusion into the non-myelosuppressed host. In the proposed clinical trial, CD 34 cells from patients with cancer will be transduced with a retrovirus derived from MFG and produced in the PG-13 cell line by the National Gene Vector Laboratory. These cells will then be re-infused into the patient after which patients will be receive cycles of BG and BCNU therapy at standard phase II doses. The objectives of this Phase I trial are: 1, Determine the feasibility of introducing and expressing mutant-MGMT-G1 56A (G156AMGMT) cDNA in hematopoietic progenitors taken from advanced solid tumor patients using the safety modified retroviral vector MFG. 2, Determine the feasibility of identification of the G156AMGMT transduced and BG & BCNU resistant hematopoietic progenitors in solid tumor patients following reinfusion. 3, Determine in vivo enrichment and longevity of the transduced progenitors during and after repeated treatments with BG & BCNU. Studies proposed in this application reflect a long term clinical goal of optimizing strategies to protect hematopoietic cells from the short and long term effects of chemotherapeutic agents. If successful, this approach could also have application in other gene therapy settings such as dual gene transfer using a therapeutic gene and stem cell organ selection.